Mobile Satellite Service User Terminals (UTs) are designed to provide voice, data and other services in a Mobile Satellite Telecommunications System (MSTS). A MSTS typically uses non-geosynchronous orbit (non-GEO) satellites, such as Low Earth Orbit (LEO) satellites, to couple signals between a ground station or gateway and a plurality of UTs. The MSTS may operate over multiple satellites at a time to provide path diversity to the UTs. The path diversity can be provided on the forward link (gateway to UT), on the return link (UT to gateway), or on both links. In general, the forward link path is power limited, and the return link path is link limited.
In MSTS systems the propagation to the UT is enhanced when path diversity is present. However, a given UT may not always experience path diversity due to blocking and shadowing effects, or due to non-uniformities in satellite constellation coverage. When the path diversity is not present, for whatever reason, the UT may find itself in a propagation environment that is sensitive to blockage, and a voice or a data call can become impaired or even dropped (i.e., abruptly terminated by the system, not the user). Unfortunately, in such a situation the user may have no idea as to why the call was impaired or dropped, or how to remedy the situation.
As such, a need exists to enable some degree of UT selectivity, control and autonomy over the operational modes and other aspects of the communications of the UT during data transfer and other types of communication operations.